An experienced tramper, he had a personal locator beacon because the area has no cellphone coverage. He set off the beacon and pulled the man as far out of the cold water as possible.
The Auckland Westpac Rescue Helicopter was contacted by the Rescue Co-ordination Centre and went to the scene but had trouble finding the exact location. Mr Walker used a signalling mirror that he was carrying to get the chopper crew's attention.
"I managed to get into some sunlight and using the heliograph mirror through a gap in the canopy I flashed the chopper. They spotted the flashing and that's how they found me."
Intensive care flight paramedic Rob Gemmell was winched down, examined the man and found he was hypotensive with a very low temperature and almost completely unconscious.
The man was yesterday in a stable condition at Auckland City Hospital.
Mr Gemmell is adamant Mr Walker's actions saved the man's life.